RO117330B1 - Process and installation for recycling waste powder coating compositions - Google Patents

Abstract

The invention relates to a process and installation for recycling waste powder coating composition. The process takes place by introducing the waste powder in an extruder, either as a base feedstock, or in addition to the feedstock components for preparing a fresh powder, extruding a feedstock into a homogenous extrudate and transforming the extrudate into a high quality powder coating composition, which consists in converting the waste powder into a layer, before feeding into the extruder, said layer being subjected to the heat at least up to a coalescence of the powder but below the decomposition or cross-linking of a part of the composition. The installation for carrying out the process comprises a vibrating plate (16), a conveyer belt (24), a heating means (20 or 30), a scrapper (28), a grinder (26) and a storage bunker (32).

Description

The present invention relates to a process for recycling the waste of powder compositions for coatings and to an installation thereof.

Waste powder compositions for coatings (hereinafter referred to as powder waste or powder coatings for coatings), as referred to herein, are waste powders that result from the preparation or application of powder coating compositions.

Powder waste results in different phases. An important source of powder waste is those obtained during the preparation of the powder. The small material (fine particles) left after the separation phase (usually with the help of a cyclone) cannot be used as coating powders (even just because they block spray pipes). Recycling of the powder that is sprayed excessively during application is generally possible within certain limits. These are undoubtedly another source of dust waste because after separation (usually with the help of a cyclone) they contain an excess of fine material that should not be reused for high quality coating. In addition, these wastes are generally impure, for example, with wastes of other colors. An analysis of waste formation can be found in K. Craine's article (Product Finishing, August 1988).

The burial or incineration of such waste are less and less accepted practices for the storage of waste in the form of powders, which has led to the need to find uses for these wastes.

We know the series of variants ("Re-use of powder coating waste", VOMINSURTEC Colloquium, Ghent, 22.03.91).

The use as a binder for solvent-based paints is contrary to the concept of reducing solvent emissions. The use of water in the preparation of the so-called "powder suspension in water" is limited to the reduced stability of the suspension.

It has also been proposed that the powdered wastes be used as a binder in the preparation of various building materials from an inert waste material (IL 9200479-A).

The above uses, however, have a lower economic interest than, the recycling of waste in the form of powders as (or in) fresh powder compositions for coatings. K. Craine's article also contains a review of some dust recovery procedures.

The direct recycling of waste in the form of powders is possible provided that a number of strict conditions are respected and limited to less important uses, such as primary coating (priming) in two-layer systems or protective coating in more applications. less demanding (for example, for storage shelves).

The recycling of powdered waste as raw material for obtaining powder for coatings is presented in DE 4028567 A. However, this use is limited to a few percent, depending on the composition of the powder and thus, the powdered waste is not fully recycled. . In addition, powders partially prepared with recycled waste tend to lead to more defects in terms of final protective coatings.

Thus, compared to the known state of the art, there is a need to develop a process for recycling the wastes of powdered compositions for coatings, in particular those made of very fine particles, which involves the use of all wastes as quality raw materials.

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The technical problem, which the invention solves, is to establish the technical conditions for the total recycling of waste in the form of powders.

The process according to the invention for the recycling of waste powders of 50 slow compositions for coating by introducing waste as a powder in an extruder, either as a base material or as an addition to the feed material components for preparing a fresh powder, extrusion of the feed material in the form of a homogeneous extrudate and the conversion of the extrudate into a higher quality coating composition, consists in the fact that, prior to feeding into the extruder 55 the powdered waste is brought in the form of a layer, with a thickness of 0.1 up to 10 mm, which is subject to the action of heat at least up to the coalescence state of the powder, but below the limit of decomposition or cross-linking of a part of the composition.

An installation for carrying out the process, according to the invention, consists of a 60 vibrating upper plate * 16 for forming the waste layer, a conveyor belt 24 for transporting the waste layer, a heating means 20 or 30 for heating the waste layer up to coalescence state, but below the decomposition or crosslinking limit, a scraper 28 for recovering coalesced material, a mill 26 for converting the material into a 65 coalescence material into granules and a storage bunker 32.

The invention has the following advantages:

- waste powder coating compositions can be introduced into processes for obtaining powder coating compositions without mixing with other raw material components; 70

- represents an ecological way of transforming waste;

- is applicable to any type of waste powder coating compositions.

Process for recycling waste powder compositions for coatings by introducing powdered waste into an extruder, either as a 75-base material or as an additive to the feed material components for preparing a fresh powder, extruding the feed material as a homogeneous extrudate and the conversion of the extrudate into a higher quality coating composition, consists in the fact that, before feeding into the extruder, the waste in powder form is brought in the form of a layer, with a thickness, from 0.1 to 10 mm, of pre-80, from 2 to 6 mm, which is subjected to the action of heat at least up to the coalescence state of the powder, but below the limit of decomposition or cross-linking of a part of the composition.

The dust layer can be formed by any means. However, it is preferred that said layer be formed on a conveyor belt. In order to obtain a uniform layer it is preferable to use a vibrating hopper. The layer may have a thickness of 0.1 ... 1.0 cm, but for practical reasons, it is recommended to form layers with a thickness of 1 ... 6 mm, preferably 2 ... 4 mm.

Heating of the waste layer in powder form can be done by any means of heating. Preferably, said layer is subjected to the action of heat 90 by using means chosen from heated rollers, infrared radiation lamps and furnaces.

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Said heating phase is followed by a phase of granular conversion of the powder, which is in the coalescence state, by grinding.

Then the granules are recycled in the process of obtaining powder compositions for coatings, as quality raw materials. It was found that while fine particles or excess particles from the spray could be difficult to recycle, within very limited limits (often with a sharp reduction in productivity and problems with the quality of the coatings being obtained), the use of granules proved to be possible within wide limits (up to the recycling of pure granules) and without problems in terms of quality. When the waste in powder form is re-introduced into an extruder as an addition to the feedstock components (ie, raw materials) raw materials that are necessary for the preparation of a fresh powder) it is observed that the addition of the granules unexpectedly allowed an increase in the extrusion yield (capacity) compared to the addition of waste in the form of powders when they are recovered for recycling. obtaining powder coating compositions is known from the prior art and is not This process is described in Powder Coatings, T.A. Misev, Wiley, 1991 (in particular, Chapter 5); Surface Coatings, S. Paul, Wiley, 1985 (in particular, Chapter 8.4); Surface Coatings, vol 2, OCCA, TAFE Educational Books, 1984 (in particular, chapter 42); The Science of Powder Coatings, D.A. Bate, SITA Technology, London, 1990.

The process according to the invention is applicable for the recycling of any waste of powdery composition. In the case of mixtures consisting of two or more compositions, their compatibility must be evaluated first.

The installation of the process consists of a top vibrating plate 16 for the formation of the waste layer, a conveyor belt 24 for the transport of the waste layer, a heating means 20 or 30 for heating the waste layer to the coalescence state, but below decomposition or cross-linking limit, a scraper 28 for recovering coalesced material, a mill 26 for transforming coalescent material into granules and a storage bunker 32.

The heating medium is chosen from heated rollers 30, infrared lamps 20 and ovens. The installation can operate continuously.

The following are two examples of embodiment of the invention in connection with FIG. 1, which represents the diagram of the installation for carrying out the process in a constructive variant in which the powder layer is pressed between a heated roller and a conveyor belt and FIG. 2, which represents the diagram of the installation for carrying out the process in a constructive variant in which the powder layer is heated by means of an infrared radiation lamp.

According to FIG. 1 the powdered waste is introduced into a hopper 10 and is uniformly dispersed on a top plate 16. The uniformity of the dispersion of the powdered waste is obtained by means well known to those skilled in the art.

For the purpose pursued by this constructive variant there is presented a vibrating plate 16. The waste material is transported on a conveyor belt 24, the flow being regulated by the variation, for example, of the amplitude of the vibration, the frequency or

RO 117330 Bl by the variation of both parameters. □ Once reached on the conveyor belt 24, the powdered waste is pressed with a heating roller 30 to form a coalescent powdered waste layer 22. At the end of the strip 24, a scraper 28 removes the material in coalescence state that falls into a mill 26 where it is transformed into granules. The granules can then be recovered and directed to a storage bunker 32.

According to FIG. 2 the powdered waste is introduced into a hopper 10 and is evenly dispersed on a vibrating top plate 16. The dusty waste layer is transported on a conveyor belt 24 over which infrared heating means are positioned. The powder reaches coalescence in the form of a layer 22 which is scraped from the strip 24 by a scraper 28, the material falling into a mill where it is transformed into granules.

The granules can then be recovered and directed to a storage bunker.

Examples 1 and 2

The following composition is used as a white powder:

- 30% by weight epoxy resin obtained from bisphenol A and epichlorohydrin and having an epoxy content of about 1350 mmol / kg, a molecular weight of about 1500 and a viscosity of about 3.5 Pa.s at 150 ° C, and 0.7 Pa.s at 175 ° C;

- 30% by weight saturated carboxylate polyester resin, having an acidity index of about 77 and a viscosity of about 1.3 Pa.s, at 165 ° C;

- 1.5% by weight additives;

- 38.5% by weight pigments and fillers.

The usual powder had the following particle distribution:

- 10% by volume below 10 ^ m;

- 50% by volume below 35 μίτι;

- 90% by volume below 70 μΐη.

Both the small material obtained during production (example 1) and the powdered waste produced during application (example 2) are collected. The chemical compositions of the wastes in the form of powders have not been verified for contamination (impurification). They presented the following distribution of

140

145

150

155

160

165 particles:

Example 1

- 10% by volume below 1 m;

- 50% by volume below 3 ^ m;

- 90% by volume below 7 μιη;

- 100% by volume below 190 μίτί. '

Example 2

- 10% by volume below 1,5 μίτι;

- 50% by volume below 7 ^ m;

- 90% by volume below 18 m; -100% by volume below 190 μπτ

170

175

Each of the wastes in powder form is heated with the aid of the installation shown in fig. 2, using infrared radiation lamps located, 36 cm from the waste layer in shape and radiating a surface with a width of 14 cm and a length of 28 cm. Infrared lamps operate at a nominal voltage of 220 V, have a power of 8000 W and are used, at 30% of the maximum voltage. 180

Layers are deposited separately on the conveyor belt, approximately 6 mm from each powdered waste, the belt moving at a speed of 14 cm / min.

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After heating, the waste in powder form goes into coalescence, then they are subjected to a coarse grinding and are returned, as feed material, to the extruder used for the preparation of fresh powder having the above mentioned composition.

The addition of 20% by weight granules in the extruded product had virtually no influence on the extrusion speed, under the following conditions, nor in terms of the fine granules from production (example 1) and those obtained during application ( example 2).

- vessel temperature: 13 ° C;

- snail temperature: 7 ° C;

- rotational speed (speed) 150 rpm,

- length / diameter ratio of snail: 7;

- extrusion capacity: 1.4 kg / min.

After grinding and sifting, the respective powders are applied to cold rolled steel plates, 1 mm thick (with a pretreatment in FePOJ and baked, for 8 minutes, at a temperature of 2OO ° C (object temperature) to obtain coatings. with a thickness of about 75 μτη; the resulting coatings have no defects.

The above examples clearly show the advantages of the process and the installation, according to the present invention. Although some specific examples of embodiments of the invention are presented in detail, this description does not limit the invention to the particular form of the examples presented here because they should be regarded as merely illustrative, but not restrictive, and for those skilled in the art it is obvious that the invention is not so. limited.

Comparative examples A and B

Powder wastes obtained during production (comparative example A) and during application (comparative example B) as described in example 1 and 2 respectively are returned directly as feed material to the extruder used to prepare the coating composition. from fresh powder.

The following extrusion rates are respected in comparative example A as well as in comparative example B, depending on the amount of added powder waste, the extrusion conditions being those described in examples 1 and 2:

% By weight 1.4 kg / min;

% by weight 1.3 kg / min;

% by weight 1.15 kg / min;

% by weight 0.9 kg / min;

% by weight 0.4 kg / min.

After grinding and screening, the powders are used to obtain the coating compositions, as shown for Examples 1 and 2.

The resulting coatings are of the same quality as those obtained in Examples 1 and 2 respectively.

These examples illustrate the advantages of the present invention.

Claims (7)

1. Waste recycling process of powder compositions for coatings by introducing waste below. powder form in an extruder, either as a base material or as an addition to the feedstock components for preparing a fresh powder, extruding the feed material as a homogeneous extrudate and converting the extrudate into a top quality coating composition, characterized in that, before feeding into the extruder, the waste in powder form is brought in the form of a layer, with a thickness, from 0.1 to 10 mm, which is subjected to the action of heat at least, until the coalescence state of the powder , but below the limit of decomposition or cross-linking of a part of the composition. 2. Process according to claim 1, characterized in that said layer is formed on a conveyor belt. 3. Process according to claims 1 or 2, characterized in that said layer is brought to a thickness between 2 and 6 mm. 4. Process according to claims 1-3, characterized in that said layer is subjected to the action of heat by means of means chosen between heated rollers, infrared radiation lamps and furnaces. 5. Process according to claims 1-3, characterized in that said heating phase is followed by a phase of granular conversion of the powder, in the coalescence state, by milling. 6. The process installation apparatus as defined in claim 1, characterized in that it consists of a top vibrating plate (16) for forming the waste layer, a conveyor belt (24) for transporting the waste layer, a heating means. (20 or 30) for heating the waste layer to the coalescence state but below the decomposition or cross-linking limit, a scraper (28) for recovering the coalescent material, a mill (26) for transforming the material into a coalescence state in granules and a storage bunker (32). Installation according to claim 6, characterized in that the heating means is chosen from heated rollers (30), infrared radiation lamps (20) and ovens.